Heroku Teams https://devcenter.heroku.com/articles/heroku-teams -- it used to be awkward to "share" deployments, or have a fake company user that owned it; teams are free for up to 5 members, then $10 per month for more. Also no free dynos for teams.
I have been using Heroku for many many years. Heroku was serverless (and containers) before either term existed. I have helped get a variety of open source software running on Heroku with DeployToHeroku, all in service of me not having to maintain a "stack" myself.